Delivery of drugs to the systemic blood of a patient by means of an electro-osmotic transdermal system is accomplished primarily through the sweat and sebaceous ducts and their respective glands rather than through the stratum corneum. The skin of humans is covered by the stratum corneum, which, although very thin, is resistant to the passage of both current and of liquids. In addition, the sweat and sebaceous ducts, when filled with liquid, become paths of least electrical resistance and in effect become shunts, and are so-called herein, for the passage of electricity and thus for the passage of drugs contained in the drug patch, bypassing the stratum corneum. These shunts extend through the stratum corneum with their duct openings being at the surface of the stratum corneum; the duct openings occupy about one thousandth of the surface of the stratum corneum. The capillary shunts are very small in diameter being in the range of 10.sup.-3 cm.sup.2 and are thus prone to being easily irritated and damaged by overheating and by excessive endosmotic pressure in the shunts by the passage of current through the shunts. Irritation of the shunts results in a tingling sensation and discomfort to the patient. Current density and the rate of drug delivery through the shunt ducts is thus limited not only by the small overall area that the shunts occupy relative to the area of the stratum corneum but also by the susceptibility of the shunts to damage because of the high current density.
Accordingly, it is an object of this invention to provide an electro-osmotic transdermal drug delivery system that primarily delivers a drug or drugs through the stratum corneum and substantially avoids drug delivery through the skin shunts so that the possibility of damage to the skin shunts is limited.
It is another object of this invention to provide an electro-osmotic transdermal drug delivery system that primarily delivers a drug or drugs through the stratum corneum so that the entire surface of the stratum corneum can be utilized for drug delivery with the result that the overall rate of drug delivery is improved as compared to the rate of drug delivery primarily through the skin shunts.
It is another object of this invention to provide an electro-osmotic transdermal drug delivery system that primarily delivers a drug or drugs through the stratum corneum so that a higher current can be used in the system than the current that could be used when drug delivery is primarily through the skin shunts with the result that the rate of drug delivery is enhanced relative to the rate of drug delivery primarily through the skin shunts.